A conventional engine cooling module is shown, generally indicated at 10, in FIG. 1 and this type of module is described in the published U.S. Patent Application No. 20070024135, the contents of which is hereby incorporated by reference into this specification. The module includes a shroud 12, and a fan 14 and motor (not seen) for driving the fan 14. The motor is enclosed inside the central shield 16 of the shroud 12. There are also dual modules 10′ as shown on FIG. 2 and these types of modules include two motors 18, two fans 14, and one shroud 12′). However, in both types of modules, the electric motor is a discrete subassembly and it is mounted on to the shroud at the center of the fan. A typical electric motor 18 used in these applications is shown in FIG. 3 (in the Patent Application No. 20070024135, shown in FIG. 6). The motor 18 includes four subassemblies: first, the stator assembly (motor case 20 with magnets 22 and ball bearing assembly 24); second, the armature assembly (assembly of shaft 26, commutator 28 and armature core 30 with copper windings (not shown)); and third, the brush card assembly 32; and fourth, the end cap assembly 34. These subassemblies are produced on dedicated assembly lines requiring a large capital investment. This is one of the disadvantages of the conventional brush type motor design.
In many new vehicle applications the shaft power (Pout) requirement of the engine cooling module is up to 800 W and considering the life/durability requirements of OEM specifications the conventional brush type motor design is not suited for such applications. Typically the brush type motors are limited to a shaft power of 400 W.
To further explain the power limitation of the conventional brush type motors the Shaft Power is defined by the following equation:Pout=T*S   (Eq. 1)
where the T=Torque [N*m] and S=Rotational Speed [radians/sec]; Therefore with increasing shaft power requirement either the torque or the speed (or both) need to be increased proportionally.
However for optimum motor life the operating torque typically is limited to 10 to 15% of stall torque. The fan speed also needs to be carefully considered since fan noise is proportional to fan speed and the OEM's specifications require low noise levels even with increased power requirements. The change of fan noise in function of change of fan speed is graphically shown on FIG. 4. The graph function is defined by Eq. 2 at equal power and fan air density and it was derived from commonly known fan laws shown on Eq. 3.L1−L2=8*log10(S1/S2)   (Eq. 2)L1−L2=14*log10(P1/P2)+8*log10(S1/S2)+6*log10(φ1/φ2)   (Eq. 3)
where L is noise (sound) power level measured
P is fan power
S is fan speed
φ is fan air density
Therefore an optimized high power module could be achieved if the motor can operate at high torque and low speed and still meet adequate motor life/durability with low sound levels.
Accordingly, there is a need to improve the engine cooling module design to reduce manufacturing cost, also can provide high power operations at high torque and low operating speed and still meet life/durability and acoustics requirements.